Optical Apparatus and Methods of Manufacture Thereof

ABSTRACT

Optical apparatus and methods of manufacture thereof An optical apparatus (20) for evanescently coupling an optical signal across an (interface (30) is described. The optical apparatus (20) comprises a first substrate (22) and a second substrate (24). The optical signal is evanescently coupled between a first waveguide (26) formed by laser inscription of the first substrate (22) and a second waveguide (28) of the second substrate (22). The first waveguide (26) comprises a curved section (34) configured to provide evanescent coupling of the optical signal between the first and second waveguides (26, 28) via the interface (30).

FIELD

Described embodiments relate to optical apparatus for routing opticalsignals, for example but not exclusively in, data communications, andmethods of manufacture of such optical apparatus.

BACKGROUND

High refractive index contrast photonic integrated circuits (PICs) haveapplications for use as transceivers for telecommunications. PICs aretypically made using platforms such as silicon or indium phosphide.Challenges exist in terms of coupling light efficiently into and out ofthe PICs with acceptable alignment tolerances, broad bandwidth and lowpolarization dependence. The high refractive index contrast of theseplatforms tends to result in relatively small mode field diameterscompared with optical fibers which deliver light into and from theplatform. The conversion efficiency between dissimilar mode sizesaffects the overall coupling performance.

Two possible approaches to providing the optical coupling includegrating couplers and edge couplers. Grating couplers comprise a periodicstructure which causes an optical signal to be diffracted at an anglerelative to the direction of the incident optical signal. Gratingcouplers produce similar mode sizes to optical fibers. However, gratingcouplers suffer from poor insertion losses, have a narrow spectralbandwidth and are restrictive in terms of the polarization of theoptical signal.

Edge couplers employ spot size converter structures fabricated on top ofthe platform to allow the mode size to be expanded to a suitable sizefor coupling into an optical fiber. Edge couplers have low alignmenttolerances and typically require the use of a lensed fiber to minimizelosses.

This background serves only to set a scene to allow a skilled reader tobetter appreciate the following description. Therefore, none of theabove discussion should necessarily be taken as an acknowledgement thatthat discussion is part of the state of the art or is common generalknowledge. One or more aspects/embodiments of the invention may or maynot address one or more of the background issues.

SUMMARY

According to an aspect or embodiment, there is provided an opticalapparatus for evanescently coupling an optical signal across aninterface between a first waveguide and a second waveguide of a secondsubstrate. Optionally, the first waveguide may be formed by laserinscription of the first substrate. The optical apparatus may comprisethe first substrate. The first waveguide may comprise a curved sectionconfigured to provide evanescent coupling of the optical signal betweenthe first and second waveguides.

According to an aspect or embodiment, there is provided an opticalapparatus. The optical apparatus may comprise a first substratecomprising a first waveguide formed by laser inscription of the firstsubstrate. The optical apparatus may comprise a second substratecomprising a second waveguide, wherein the first waveguide comprises acurved section configured to provide evanescent coupling of an opticalsignal across an interface between the first and second waveguides.

In use, the optical apparatus may be configured to route an opticalsignal across the interface, for example, as part of a transceiver orother communication apparatus in which different optical characteristicsin different parts of the transceiver or other communication apparatusmay otherwise cause issues in terms of inefficient coupling of theoptical signal therebetween. For example, the first and secondwaveguides may have different refractive indices.

The use of a glass or amorphous material in one embodiment as the firstsubstrate may provide at least one of: improved performance,manufacturability and compatibility with photonic integrated circuit(PIC) platforms. PIC platforms and silica may have similar thermalexpansion coefficients, and may be considered to be reliable and/ormechanical stable. The possibility to use 3D laser-inscribed waveguidesmay provide design freedoms (e.g. by utilizing the third dimension),which may improve performance and/or ease of manufacturability.

Embodiments described herein may have improved alignment tolerancescompared with other approaches. The evanescent coupling approach mayprovide lower polarization dependence compared with other approaches.The optical apparatus may be relatively straightforward to manufactureand/or may not require any form of polishing in certain embodiments.

In some embodiments, the first waveguide may be coupled to an opticalfiber (e.g. a standard optical fiber, or the like). In spite of thepotentially different optical mode sizes of the optical fiber and thesecond waveguide, the design of the first waveguide may be such that atleast one of: low insertion losses, broad spectral bandwidthtransmission, low polarization dependence and relaxed alignmenttolerances may be achieved.

By providing a curved section in the first waveguide, the evanescentfield in the coupling region may be increased compared with non-curvedwaveguides. The curved section may provide improved optical couplingefficiency between the first and second waveguides compared with othermethods for coupling optical signals between different waveguides. Thecurved section may allow the resulting evanescent field to propagateover a sufficient distance to permit additional layers to be providedbetween the first and second waveguides compared with if no curvedsection is provided. The distance of propagation facilitated by thecurved section may allow the first waveguide to be inscribed in thefirst substrate proximal to the interface without, in some embodiments,necessarily forming part of the interface.

Some optional features of the aspect or embodiment are set out below.

The curved section may be proximal to the interface.

The interface may comprise or refer to a surface of the first substrate.The curved section may be positioned relative to the surface such that,in operation, the optical signal may be evanescently coupled between thefirst and second waveguides. The curvature of the curved section may beselected such as to provide, in operation, evanescent coupling of theoptical signal between the first and second waveguides. For example, aradius of curvature and/or radius of curvature may vary as function ofposition along the first waveguide may be selected such as to provideevanescent coupling of the optical signal.

The curvature may affect the strength of the evanescent coupling. Insome embodiments, a first radius of curvature may be selected such thatan evanescent field propagates over a first distance between acenterline of the first and second waveguides. In some otherembodiments, a second radius of curvature may be selected such that anevanescent field propagates over a second distance between a centerlineof the first and second waveguides, wherein the second radius ofcurvature is less than the first radius of curvature and the seconddistance is greater than the first distance. Thus, the curvature of thecurved section may be selected according to the distance between thecenterlines of the first and second waveguides such that the opticalsignal may be evanescently coupled therebetween.

The curved section may extend in a plane parallel to a propagationdirection of the evanescently coupled optical signal. The plane may beperpendicular to the interface. The curved section may be curved withrespect to the surface such that the first waveguide is spaced from thesurface. The spacing of the first waveguide from the surface may be suchthat a spatial extent (e.g. a transverse cross section of the firstwaveguide, or the like) of the first waveguide does not extend throughthe surface. The spacing between the centerline of the first waveguideand the surface may be less than 100 μm, less than 50 μm, less than 25μm, less than 10 μm, less than 5 μm, less than 2 μm, less than 1 μm,and/or more than 10 nm, more than 25 nm, more than 50 nm, more than 100nm, more than 0.5 μm, or the like. In an example of a laser-inscribedfirst waveguide, the spacing between a centerline of the first waveguideand the surface may be greater than a radius of the first waveguidealong the centerline thereof.

The first waveguide may further comprise a straight section adjacent tothe curved section and proximal to the interface. The first waveguidemay be positionable relative to the second waveguide such that thestraight section is parallel to a proximal portion of the secondwaveguide. A radius of curvature of the curved section may be defined bya geometrical relation between a portion of the first waveguide distalto the interface and a portion of the first waveguide proximal to theinterface. The portion of the first waveguide proximal to the interfacemay be shaped such that an evanescent field of the optical signal may bepermitted to propagate through the portion between the first and secondwaveguides. The curvature of the curved section may be selected suchthat an evanescent field extends through the interface.

The first waveguide may define a three-dimensional structure. Acenterline of the first waveguide may extend in two or three dimensions.For example, the centerline may extend through a curved path in a planeperpendicular to the surface. In Cartesian coordinates, the centerlinemay extend in the two or more different directions selected from the X,Y and Z directions. The first waveguide may be formed in any way suchthat the centerline of the first waveguide follows nonlinear paththrough the first substrate.

The first substrate may comprise at least one of: a glass; and amorphousmaterial.

The first waveguide may be configured to provide adiabatic evanescentcoupling of the optical signal between the first and second waveguides.The first waveguide may comprise at least one characteristic along thewaveguide for providing adiabatic evanescent coupling. The firstwaveguide may have at least one characteristic that varies along thefirst waveguide. For example, at least one of: transverse size, shape,refractive index, and the like may vary as function of position alongthe first waveguide.

The first waveguide may be configured such that at least onephase-matching region is configured such that a propagation constant ofthe first waveguide is the same as a propagation constant of the secondwaveguide. The first waveguide may comprise at least one taperedsection. The tapered section may comprise at least one phase-matchingregion. The characteristic along the first waveguide may comprise atleast one phase-matching region.

A refractive index of the first waveguide may vary as function ofposition along the first waveguide.

The first waveguide may have a refractive index contrast withsurrounding material of the first substrate that varies as function ofposition along the first waveguide. The refractive index contrast mayrefer to a different between the refractive index of the surroundingmaterial and the refractive index of the first waveguide. The refractiveindex of the first waveguide may typically be higher than the refractiveindex of the surrounding material.

The first waveguide may be configured such that the refractive index ofpart or all of the first waveguide varies, e.g. continuously varies, ina first direction and/or a second direction. The first direction maycomprise a direction along the first waveguide, e.g. a propagationdirection of the optical signal in the first waveguide. The seconddirection may comprise a direction that is perpendicular to the firstdirection. For example, the first waveguide may be configured such thatthe refractive index of part or all of the first waveguide may decreasein the first direction and/or the second direction. Alternatively oradditionally, the first waveguide may be configured such that therefractive index of part or all of the first waveguide may increase inthe first direction and/or the second direction. The refractive index ofpart or all of the first waveguide may be varied, e.g. continuouslyvaried, in the first direction and/or the second direction, by varying,e.g. continuously varying, the refractive index contrast between part orall of first waveguide and the surrounding material. The refractiveindex of part or all of the first waveguide may be varied using laserinscription of the first substrate. By using laser inscription of thefirst substrate, the formation of a first waveguide comprising arefractive index that may vary, e.g. continuously vary, may befacilitated.

The optical apparatus may comprise a further waveguide for providingevanescent coupling between the first waveguide and the secondwaveguide. The further waveguide may comprise at least one of: siliconoxynitride; germanium doped silica; and silicon nitride.

The optical apparatus may further comprise the second substrate. Thesecond waveguide of the second substrate may comprise a material ofhigher refractive index than the first waveguide and the furtherwaveguide. The further waveguide may comprise a material having a higherrefractive index than the first waveguide.

The optical apparatus may comprise the second substrate. The secondwaveguide of the second substrate may comprise a material of higherrefractive index than the first waveguide. The material of the secondwaveguide may comprise at least one of: silicon; silicon nitride; andindium phosphide.

The second waveguide may be configured to provide adiabatic evanescentcoupling of the optical signal between the first and second waveguides.The second waveguide may be configured such that the second waveguidemay comprise at least one phase-matching region configured such that apropagation constant of the second waveguide is the same as apropagation constant of the first waveguide. The second waveguide maycomprise at least one tapered section. The tapered section may compriseat least one phase-matching region. The second waveguide may comprise atleast one characteristic along the second waveguide for providingadiabatic evanescent coupling.

The tapered section may be configured such that a width or thickness ofthe tapered section varies, e.g. continuously varies, in a firstdirection and/or a second direction. The first direction may comprise adirection along the second waveguide, e.g. a propagation direction ofthe optical signal in the second waveguide. The second direction maycomprise a direction that is perpendicular to the first direction. Forexample, the tapered section may be configured such that the width ofthe tapered section increases or decreases in the first direction and/orthe second direction.

For example, when the width or thickness of the tapered sectionincreases in the first direction and/or the second direction, the secondwaveguide may comprise a constricted section. The constricted sectionmay comprise a width or thickness, e.g. in the first direction and/orthe second direction, that is smaller or narrower than a width orthickness of the tapered section, e.g. in the first direction and/or thesecond direction. The constricted section may be arranged spaced or at adistance from the tapered section of the second waveguide. Theconstricted section may be configured to filter one or more modes of theoptical signal. The constricted section may be arranged to allowtransmission of a single mode of the optical signal into the taperedsection of the second waveguide.

The second waveguide may be configured to comprise a plurality of partsor segments. The plurality of parts or segments may be arranged alongthe first direction. Some or all parts or segments of the plurality ofparts or segments may comprise the same refractive index or refractiveindex contrast with the surrounding material. The plurality of parts orsegments may be arranged such that a refractive index of the secondwaveguide varies in the first direction and/or the second direction. Forexample, the second waveguide may be configured such that a size orwidth of some or all parts or segments of the plurality of parts orsegments varies, e.g. decreases or increases, in the first directionand/or the second direction. The second waveguide may be configured suchthat a space or distance between at least two or all parts or segmentsof the plurality of parts or segments varies, e.g. decreases orincreases, in the first direction.

The second waveguide may be configured such that a size or width of someor all parts or segments of the plurality of parts or segments is thesame. The second waveguide may be configured such that a space ordistance between at least two or all parts or segments of the pluralityof parts or segments is the same. The second waveguide may be configuredsuch that the size or width of some or all of the parts or segments ofthe plurality of parts or segment is smaller than a wavelength of theoptical signal. The second waveguide may be configured such that thespace or distance between at least two or all parts or segments of theplurality of parts or segment is smaller than a wavelength of theoptical signal. Some or all of the plurality of parts or segments may bearranged along the second direction. For example, the plurality of partsor segments may be arranged to form an array of parts or segments. Someor all of the plurality of parts or segments may be considered asforming a metamaterial. The plurality of parts or segments may bearranged to vary, e.g. decrease or increase, the refractive index, e.g.the effective refractive index, of the second waveguide.

It will be appreciated that the first waveguide, e.g. the taperedsection thereof, may comprise any of the features of the secondwaveguide and/or the tapered section of the second waveguide.

The optical apparatus may comprise an electrical component configured toat least one of: convert the optical signal into an electrical signal;and convert an electrical signal into the optical signal.

The electrical component may be configured to at least one of: transmit;and receive the optical signal via the second waveguide.

The electrical component may be configured to at least one of: transmit;and receive the optical signal such that the optical signal is routedbetween the first and second waveguides.

The optical apparatus may comprise a carrier configured to provide atleast one of: optical, electrical and magnetic communication with theelectrical component.

The first substrate may be disposed between the second substrate and thecarrier.

The first substrate may comprise at least one via extending therethroughbetween the second substrate and the carrier.

The optical apparatus may comprise a carrier operative to communicatewith an electrical component of the second substrate using an electricalsignal. The first substrate may be disposed between the second substrateand the carrier. The first substrate may comprise at least one viaextending therethrough between the second substrate and the carrier. Theelectrical component may be operative to convert received one of: theoptical signal and the electrical signal into the other one of: theoptical signal and the electrical signal.

The second waveguide may comprise a splitter. The splitter may comprisea plurality of transversely spaced apart tapered sections. The taperedsections may be configured to provide adiabatic evanescent coupling withthe first waveguide.

The optical apparatus may comprise at least one spacing element disposedbetween the first and second substrates. The at least one spacingelement may comprise one of: silicon oxynitride; silicon dioxide; andsilicon nitride. The optical apparatus may comprise a further waveguidedisposed between the first and second substrates for providingevanescent coupling between the first waveguide and the second waveguidevia the further waveguide. The optical apparatus may comprise at leastone recessed region in at least one layer disposed between the first andsecond substrates. The at least one spacing element may be provided inthe at least one recessed region.

The optical apparatus may comprise a further waveguide for providingevanescent coupling with the first waveguide. The further waveguide maybe provided in a removed portion of a sacrificial layer deposited on thefirst substrate.

Alternatively, the further waveguide may be formed on a conditioned orprepared surface of the first substrate. The surface of the firstsubstrate may be conditioned or prepared, e.g. prior to the furtherwaveguide being formed, such that an amount of defects or particles onthe first substrate is reduced.

The further waveguide may be configured to provide adiabatic evanescentcoupling of the optical signal between the first and further waveguides.The further waveguide may be configured such that the further waveguidemay comprise at least one phase-matching region configured such that apropagation constant of the further waveguide is the same as apropagation constant of the first waveguide. The further waveguide maycomprise at least one tapered section. The tapered section may compriseat least one phase-matching region. The optical apparatus may furthercomprise the second substrate, the further waveguide being providedbetween the first and second substrates and configured for providingevanescent coupling between the first waveguide and the second waveguidevia the further waveguide. Alternatively or additionally, the furtherwaveguide may be configured for providing evanescent coupling with thesecond waveguide. The further waveguide may comprise at least onecharacteristic along the further waveguide for providing adiabaticevanescent coupling of the optical signal between the first and furtherwaveguides. The characteristic along the further waveguide may compriseat least one phase-matching region.

A radius of curvature of the curved section may vary as function ofposition along the first waveguide.

The tapered section may be configured such that a width or thickness ofthe tapered section varies, e.g. continuously varies, in a firstdirection and/or a second direction. The first direction may comprise adirection along the further waveguide, e.g. a propagation direction ofthe optical signal in the further waveguide. The second direction maycomprise a direction that is perpendicular to first direction. Forexample, the tapered section may be configured such that the width orthickness of the tapered section increases or decreases in the firstdirection and/or the second direction.

For example, when the width or thickness of the tapered sectionincreases in the first direction and/or the second direction, thefurther waveguide may comprise a constricted section. The constrictedsection may comprise a width or thickness, e.g. in the first directionand/or the second direction, e.g. that is smaller or narrower than awidth or thickness of the tapered section, e.g. in the first directionand/or the second direction. The constricted section may be arrangedspaced or at a distance from the tapered section of the furtherwaveguide. The constricted section may be configured to filter one ormore modes of the optical signal. The constricted section may bearranged to allow transmission of a single mode of the optical signalinto the tapered section of the further waveguide.

The further waveguide may be configured to comprise a plurality of partsor segments. The plurality of parts or segments may be arranged in alongthe first direction of further waveguide. Some or all parts or segmentsof the plurality of parts or segments may comprise the same refractiveindex or refractive index contrast with the surrounding material. Theplurality of parts or segments may be arranged such that a refractiveindex of the further waveguide varies in the first direction and/or thesecond direction. For example, the further waveguide may be configuredsuch that a size or width of some or all parts or segments of theplurality of parts or segments varies, e.g. decreases or increases, inthe first direction and/or the second direction. The further waveguidemay be configured such that a space or distance between at least two orall parts or segments of the plurality of parts or segments varies, e.g.decreases or increases, in the first direction.

The further waveguide may be configured such that a size or width ofsome or all parts or segments of the plurality of parts or segments isthe same. The further waveguide may be configured such that a space ordistance between at least two or all parts or segments of the pluralityof parts or segments is the same. The further waveguide may beconfigured such that the size or width of some or all of the parts orsegments of the plurality of parts or segment is smaller than awavelength of the optical signal. The further waveguide may beconfigured such that the space or distance between at least two or allparts or segments of the plurality of parts or segment is smaller than awavelength of the optical signal. Some or all of the plurality of partsor segments may be arranged along the second direction. For example, theplurality of parts or segments may be arranged to form an array of partsor segments. Some or all of the plurality of parts or segments may beconsidered as forming a metamaterial. The plurality of parts or segmentsmay be arranged to vary, e.g. decrease or increase, the refractiveindex, e.g. the effective refractive index, of the further waveguide.

It will be appreciated that the first waveguide, e.g. the taperedsection thereof, may comprise any of the features of the furtherwaveguide and/or the tapered section of the second waveguide.

The optical apparatus may comprise at least one opening. The opening maybe part of or comprised in the first substrate. The opening may compriseor be provided in the form of a channel, hole, through-hole, vent or thelike. The opening may be arranged to allow passage of gas from a spacebetween the first substrate and the second substrate, e.g. when thefirst and second substrates are coupled together. The opening may bearranged to allow passage of a bonding material into at least part ofthe opening, e.g. when the first and second substrates are coupledtogether.

At least one of the first substrate and the second substrate may beconfigured or shaped to allow for coupling, e.g. complementarilycoupling, with at least one other of the first substrate and the secondsubstrate. For example, at least one of the first substrate and thesecond substrate may be shaped or configured to allow for butt couplingbetween the further waveguide, e.g. provided on the first substrate, andthe second waveguide. The at least one of the first substrate and thesecond substrate may comprise an edge or periphery. The edge orperiphery may be shaped to match, e.g. complementarily match, a furtheredge of the at least one other of the first substrate and secondsubstrate. In other words, at least one of the edge and further edge maybe shaped or configured such that the at least one of the edge and thefurther edge and the at least one other of the edge and further edgedefine opposing edges, e.g. to allow for complementary coupling togetherof the first substrate and the second substrate. This may allow for thefurther waveguide being brought into close proximity of the secondwaveguide, e.g. thereby reducing a distance between the furtherwaveguide and the second waveguide, which may reduce losses of theoptical signal over the distance between the further waveguide and thesecond wave guide. The second substrate may comprise a coupling portion.The coupling portion may comprise or be provided in the form of an edgecoupler or edge coupling portion. The coupling portion may be arrangedto allow for butt coupling between the further waveguide and the secondwaveguide, e.g. when the first substrate and second substrate arecoupled together. The further waveguide may be arranged relative to thesecond waveguide such that a propagation direction of the optical signalin the further waveguide corresponds to or is the same as a propagationdirection of the optical signal in the second waveguide, e.g. when thefirst substrate and second substrate are coupled together.

One or more of the above optional features may be provided incombination with or replace at least one corresponding feature in theaspects or embodiments set out below. The features relating to apparatusmay be equally applied to methods, as appropriate and vice versa.

According to an aspect or embodiment there is provided a communicationapparatus for routing an optical signal. The communication apparatus maycomprise the optical apparatus of any aspect or embodiment describedherein. The communication apparatus may comprise or configured tofunction as a transceiver, transmitter and/or receiver. Thecommunication apparatus may comprise an optical communication deviceconfigured for optical communication with the first waveguide. Theoptical communication device may comprise a transceiver, receiver,transmitter, or the like. The optical communication device may becoupled to the first waveguide via at least one optical fiber. Thecommunication apparatus may comprise an electrical component configuredto provide electrical, optical and/or magnetic communication with thesecond waveguide. In operation, data may be communicated via optical,electrical and/or a magnetic signal such that an optical signal carryingor representative of the data may be routed between the first and secondwaveguides via evanescent coupling. The communication apparatus mayconvert a data carrying signal between one or more forms (e.g. optical,electrical, magnetic, or the like) such that an optical communicationdevice and an electrical communication device may communicate the data.

According to an aspect or embodiment there is provided a method ofmanufacturing an optical apparatus for evanescently coupling an opticalsignal across an interface between a first waveguide, optionally formedby laser inscription of a first substrate, and a second waveguide of asecond substrate. The method may comprise providing the first substrate.The method may comprise forming the first waveguide to comprise a curvedsection configured to provide evanescent coupling of the optical signalbetween the first and second waveguides.

According to an aspect or embodiment there is provided a method ofmanufacturing an optical apparatus. The method may comprise providing afirst substrate. The method may comprise forming a first waveguide inthe first substrate by laser inscription so that the first waveguidecomprises a curved section. The method may comprise providing a secondsubstrate comprising a second waveguide. The method may comprisecoupling the first substrate and second substrate together so that thecurved section is configured to provide evanescent coupling of anoptical signal across an interface between the first waveguide and thesecond waveguide.

The method may comprise providing a further waveguide between the firstand second substrates for providing evanescent coupling between thefirst waveguide and the second waveguide.

The method may comprise forming the further waveguide on a surface ofthe first substrate and/or second substrate.

The method may comprise preparing or conditioning the surface of thefirst substrate and/or second substrate, e.g. to reduce an amount ofdefects, such as for example cracks or microcracks, and/or particles onthe surface.

The method may comprise preparing or conditioning the surface of thefirst substrate and/or second substrate prior to forming the furtherwaveguide.

The method may comprise forming the first waveguide after coupling thefirst and second substrates together.

The method may comprise forming the first waveguide prior to couplingthe first and second substrates together.

The method may comprise coupling the first substrate and the secondsubstrate together using a welding technique, such as laser beamwelding.

According to an aspect or embodiment there is provided a method of usingan optical apparatus for evanescently coupling an optical signal acrossan interface between a first waveguide, optionally formed by laserinscription, of a first substrate and a second waveguide of a secondsubstrate. The method may comprise transmitting an optical signalthrough a curved section of the first waveguide so as to evanescentlycouple the optical signal between the first and second waveguides.

According to an aspect or embodiment there is provided an opticalapparatus for evanescently coupling an optical signal across aninterface. The optical apparatus may comprise a first substratecomprising a first waveguide, optionally formed by laser inscription.The optical apparatus may comprise a second substrate comprising asecond waveguide. The first waveguide may comprise a curved sectionconfigured to provide evanescent coupling of the optical signal betweenthe first and second waveguides.

According to an aspect or embodiment there is provided a method ofmanufacturing an optical apparatus for evanescently coupling an opticalsignal across an interface. The method may comprise providing a firstsubstrate. The method may comprise forming a first waveguide by laserinscription of the first substrate. The method may comprise providing asecond substrate comprising a second waveguide. The method may compriseforming the first waveguide to comprise a curved section configured toprovide evanescent coupling of the optical signal between the first andsecond waveguides.

According to an aspect or embodiment there is provided optical apparatusfor evanescently coupling an optical signal across an interface. Theoptical apparatus may comprise a first substrate, optionally comprisinga first waveguide formed by laser inscription of the first substrate.The optical apparatus may comprise a further waveguide. The firstwaveguide may comprise a curved section configured to provide evanescentcoupling of the optical signal between the first and further waveguides.

The further waveguide may allow fabrication of compact photoniccomponents with substantially higher refractive index contrast comparedwith solely the laser inscribed first waveguide and the secondwaveguide, as described herein. The optical apparatus may benefit fromlow loss coupling to the laser-inscribed first waveguide for furtherintegration and low loss interfacing to optical fibers. Exampleapplications may include the fabrication of wavelengthmultiplexer/demultiplexer circuits on the surface waveguide layers,which may be too large to fabricate with the lower refractive indexcontrast available with other laser inscribed waveguides, or the like.

The further waveguide may be used to allow low-loss efficient buttcoupling to edge based spot size conversion couplers fabricated on highrefractive index contrast platforms such as those made in SiliconPhotonics or Indium Phosphide, or the like.

One possible application of using the further waveguide may be to act asan intermediate layer in evanescently coupling to high refractive indexcontrast platforms. In one example, the further waveguide may help toefficiently transfer the light from the first waveguide into a highrefractive index contrast second waveguide. This approach may providefor high coupling efficiencies. Design simulations indicate that totalevanescent coupling efficiencies may be above 95%.

Some optional features of the aspect or embodiment are set out below.

The further waveguide may comprise a material of higher refractive indexthan the first substrate.

The further waveguide may comprise at least one of: silicon oxynitride;germanium doped silica; and silicon nitride.

The further waveguide may be formed by forming, e.g. etching, a patternin a waveguide layer deposited on the first substrate.

One or more of the above optional features may be provided incombination with or replace at least one corresponding feature in theaspects or embodiments set out below. The features relating to apparatusmay be equally applied to methods, as appropriate and vice versa.

According to an aspect or embodiment there is provided a communicationapparatus for routing an optical signal. The communication apparatus maycomprise the optical apparatus of any aspect or embodiment describedherein.

According to an aspect or embodiment there is provided a method ofmanufacturing an optical apparatus for evanescently coupling an opticalsignal across an interface. The method may comprise providing a firstsubstrate. The method may comprise forming a first waveguide by laserinscription of the first substrate. The method may comprise providing afurther waveguide. The method may comprise forming the first waveguideto comprise a curved section configured to provide evanescent couplingof the optical signal between the first and further waveguides.

According to an aspect or embodiment there is provided optical apparatusfor evanescently coupling an optical signal across an interface. Theoptical apparatus may comprise a substrate comprising a waveguidecomprising a curved section. The optical apparatus may comprise afurther waveguide. The curved section of the waveguide and the furtherwaveguide may be configured to provide evanescent coupling of theoptical signal between the waveguide and the further waveguide.

Some optional features of the aspect or embodiment are set out below.

The substrate may comprise one of: a first and second substrate. Theoptical apparatus may further comprise the other one of: the first andsecond substrate.

One or more of the above optional features may be provided incombination with or replace at least one corresponding feature in theaspects or embodiments set out below. The features relating to apparatusmay be equally applied to methods, as appropriate and vice versa.

According to an aspect or embodiment there is provided a method ofmanufacturing an optical apparatus for evanescently coupling an opticalsignal across an interface. The method may comprise providing asubstrate comprising a waveguide comprising a curved section. The methodmay comprise providing a further waveguide. The curved section of thewaveguide and the further waveguide may be configured to provideevanescent coupling of the optical signal between the waveguide and thefurther waveguide.

According to an aspect or embodiment there is provided optical apparatusfor evanescently coupling an optical signal across an interface. Theoptical apparatus may comprise a first substrate comprising a firstwaveguide optionally formed by laser inscription of the first substrate.The optical apparatus may comprise a second substrate comprising asecond waveguide. The optical apparatus may comprise a further waveguideprovided between the first and second substrate. The first, second andfurther waveguides may be configured to provide evanescent couplingbetween the first and second waveguides via the interface.

The first waveguide may comprise a curved section configured to provideevanescent coupling of the optical signal between the first and secondwaveguides.

According to an aspect or embodiment there is provided a method ofmanufacturing an optical apparatus for evanescently coupling an opticalsignal across an interface. The method may comprise providing a firstsubstrate. The method may comprise forming a first waveguide by laserinscription of the first substrate. The method may comprise providing asecond substrate comprising a second waveguide. The method may compriseproviding a further waveguide between the first and second substrate.The first, second and further waveguides may be configured to provideevanescent coupling between the first and second waveguides via theinterface.

According to an aspect or embodiment there is provided a method ofmanufacturing an optical apparatus. The method may comprise providing afirst substrate. The method may comprise laser inscribing a firstwaveguide in the first substrate. The method may comprise depositing awaveguide layer on the first substrate. The method may comprise forminga further waveguide from the waveguide layer.

Some optional features of the aspect or embodiment are set out below.

The method may comprise laser inscribing the first waveguide prior todepositing the waveguide layer.

The method may comprise laser inscribing the first waveguide subsequentto depositing the waveguide layer.

The method may comprise forming, e.g. etching, the waveguide layer suchthat the waveguide layer comprises different thicknesses at differentlocations in the waveguide layer.

The method may comprise depositing a cladding material on the waveguidelayer and exposed portions of the first substrate. The method maycomprise controlling the deposition of the cladding material such thatat least one portion of the waveguide layer is exposed. The method maycomprise removing a portion of the cladding material after depositionsuch that a portion of the waveguide layer is exposed. The method maycomprise allowing the cladding material to be used as an interposersubstrate for providing evanescent coupling between the claddingmaterial and the further waveguide. The method may comprise introducingstress-controlled layers on the cladding material.

The method may comprise introducing stress-controlled layers on asurface of the first substrate.

The cladding material may comprise at least one of: a glass; andamorphous material.

The method may comprise providing a layer of bonding material on thecladding material and on at least one exposed portion of the waveguidelayer.

The method may comprise removing excess bonding material.

The method may comprise coupling a second substrate to the layer ofbonding material.

The second substrate may comprise a silicon substrate and a silica layerdeposited thereon for bonding to the layer of bonding material.

The second substrate may comprise a second waveguide for positioning inthe layer of bonding material.

The method may comprise forming a pattern in the waveguide material toform the further waveguide and at least one spacing element. The methodmay comprise depositing a cladding material on the further waveguide andexposed portions of the first substrate. The method may compriseproviding a layer of bonding material on the cladding material such thatthe at least one spacing element protrudes from the layer of bondingmaterial.

The method may comprise providing a second substrate comprising at leastone recess formed on a surface thereof; and aligning the at least onespacing element in the corresponding at least one recess so as to permitthe first and second substrates to be coupled together.

The second substrate may comprise a silicon substrate and a silica layerdeposited thereon for bonding to the layer of bonding material.

The second substrate may comprise a second waveguide for positioning inthe layer of bonding material.

The method may comprise depositing a sacrificial layer on the firstsubstrate. The method may comprise laser inscribing the first waveguidein the first substrate. The method may comprise removing a portion ofthe sacrificial layer. The method may comprise depositing the waveguidelayer on a remaining portion of the sacrificial layer and exposedportions of the first substrate. The method may comprise removing one ormore parts of the waveguide layer, e.g. etching the waveguide layer, toform the further waveguide.

The sacrificial material may comprise a cladding material.

The method may comprise spin coating glass frit onto the first substrateprior to deposition of the material for forming the further waveguide.

The method may comprise planarizing at least one surface of the opticalapparatus. Planarizing may comprise using chemical-mechanical polishing(CMP) or the like.

One or more of the above optional features may be provided incombination with or replace at least one corresponding feature in theaspects or embodiments set out below. The features relating to apparatusmay be equally applied to methods, as appropriate and vice versa.

According to an aspect or embodiment there is provided a method ofmanufacturing an optical apparatus. The method may comprise providing asubstrate. The method may comprise depositing a layer on the substrate.The method may comprise laser inscribing a waveguide into the substrateproximal to an interface between the substrate and the layer.

According to an aspect or embodiment there is provided optical apparatusfor evanescently coupling an optical signal across an interface betweena first waveguide formed by laser inscription of a first substrate andan additional waveguide. The optical apparatus may comprise the firstsubstrate. The first waveguide may comprise a curved section configuredto provide evanescent coupling of the optical signal between the firstwaveguide and the additional waveguide.

The additional waveguide may comprise at least one of: a furtherwaveguide deposited on the first substrate; and a second waveguide of asecond substrate.

According to an aspect or embodiment there is provided a method ofmanufacturing an optical apparatus. The method may comprise providing afirst substrate. The method may comprise depositing a sacrificial layeron the first substrate. The method may comprise laser inscribing thefirst waveguide in the first substrate. The method may comprise removinga portion of the sacrificial layer to expose a portion of the firstsubstrate. The method may comprise providing a further waveguide on theexposed portion of the first substrate.

Providing the further waveguide may comprise depositing a waveguidelayer on at least one of: a remaining portion of the sacrificial layerand the exposed portion of the first substrate. Providing the furtherwaveguide may comprise removing one or more part from the waveguidelayer, e.g. etching the waveguide layer, to form the further waveguide.

The method may comprise providing a second substrate comprising a secondwaveguide. The first waveguide may be configured such that the firstwaveguide may comprise a curved section configured to provide evanescentcoupling of an optical signal across an interface between the firstwaveguide and the second waveguide, and via the further waveguide.

The laser inscribing step may be performed one of: before thesacrificial layer is deposited on the first substrate; and after thesacrificial layer is deposited on the first substrate.

The invention includes one or more corresponding aspects, embodiments orfeatures in isolation or in various combinations whether or notspecifically stated (including claimed) in that combination or inisolation. As will be appreciated, features associated with particularrecited embodiments relating to apparatus may be equally appropriate asfeatures of embodiments relating specifically to methods of operation,manufacture or use, and vice versa.

The above summary is intended to be merely exemplary and non-limiting.

BRIEF DESCRIPTION

A description is now given, by way of example only, with reference tothe accompanying drawings, in which:

FIG. 1 shows a cross-sectional schematic view of a photonic integratedcircuit (PIC) platform;

FIG. 2 shows a first cross-sectional schematic view of an opticalapparatus integrated with the PIC platform of FIG. 1 according to anembodiment;

FIG. 3 shows a second, orthogonal cross-sectional schematic view of theoptical apparatus and PIC platform of FIG. 2;

FIG. 4 shows a first cross-sectional schematic view of an opticalapparatus configured according to a further embodiment;

FIG. 5 shows a second, orthogonal cross-sectional schematic view of theoptical apparatus of FIG. 4;

FIGS. 6a-6b show plan views of example waveguide configurations;

FIG. 7 shows a first cross-sectional schematic view of the opticalapparatus of FIG. 4 integrated with the PIC platform of FIG. 1 accordingto an embodiment;

FIG. 8 shows a second, orthogonal cross-sectional schematic view of theoptical apparatus and PIC platform of FIG. 7;

FIG. 9 shows a cross-sectional schematic view of an assembly of anoptical apparatus, PIC platform and printed circuit board (PCB)according to an embodiment;

FIG. 10 shows a cross-sectional view of an example waveguideconfiguration for use in the optical apparatus of any embodimentdescribed herein;

FIG. 11 shows a cross-sectional view of a further example waveguideconfiguration for use in the optical apparatus of any embodimentdescribed herein;

FIG. 12 shows cross-sectional views of an example waveguideconfigurations for use in the PIC platform of any embodiment describedherein;

FIG. 13 shows a cross-sectional view of a further example waveguideconfiguration for use in the PIC platform of any embodiment describedherein;

FIG. 14 shows a cross-sectional view of an example waveguideconfiguration for use in the PIC platform of any embodiment describedherein;

FIG. 15 shows a cross-sectional schematic view of an optical apparatusconfigured to be integrated with a PIC platform according to a furtherembodiment;

FIG. 16 shows a cross-sectional schematic view of an optical apparatusconfigured to be integrated with a PIC platform according to a furtherembodiment;

FIG. 17 shows a schematic of a manufacturing process according to anembodiment;

FIGS. 18a to 18d show cross-sectional views of exemplary waveguideconfigurations;

FIG. 18e shows a plan view of an exemplary waveguide configuration;

FIG. 18f shows a cross-sectional view of an exemplary waveguideconfiguration;

FIG. 19 shows a cross-sectional schematic view of an optical apparatusaccording to an embodiment; and

FIG. 20 shows a cross-sectional schematic view of an optical apparatusaccording to an embodiment.

DETAILED DESCRIPTION

FIG. 1 shows a cross-sectional schematic view of a photonic integratedcircuit (PIC) platform 10. In this embodiment, the PIC platform 10 is inthe form of silicon-on-insulator (SOI) structure. The PIC platform 10comprises a silicon layer 12 on top of an underlayer 14 formed of SiO2(silica) deposited on top of a bulk substrate 16 comprising silicon. Thesilicon layer 12 provides a high refractive index contrast opticalwaveguide. A cladding material (in this embodiment, SiO2) 18 isdeposited on the silicon layer 12. In this example, the silicon layer 12is 220 nm thick and the underlayer 14 is 2 μm thick. It will beappreciated that any appropriate materials may be used for the PICplatform 10 and the particular configuration, number of layers and layerthicknesses may be varied as appropriate.

FIG. 2 shows a first cross-sectional schematic view of an opticalapparatus 20 integrated with the PIC platform 10 of FIG. 1. The opticalapparatus 20 comprises a first substrate 22 and a second substrate 24.In this embodiment, the first substrate 22 is made of a glass oramorphous material. However, it will be appreciated that any appropriatematerial or combination of materials may be used for the first substrate22. The first substrate 22 comprises a first waveguide 26 formed bylaser inscription of the first substrate 22. One example of a method forforming waveguides by laser inscription is described in WO 2008/155548,the content of which is hereby incorporated by reference in itsentirety. Laser inscription can be used to produce arbitrarily shapedtwo-dimensional and three-dimensional waveguides in, for example,silica.

In this embodiment, the second substrate 24 comprises the PIC platform10. The second substrate 24 comprises a second waveguide 28, which inthis embodiment is in the form of the silicon layer 12. In the region ofthe second waveguide 28, the cladding material 18 is removed or leftunpatterned, allowing the second waveguide 28 to be brought into closeproximity with the first waveguide 26. The first waveguide 26 is laserinscribed along the first substrate 22 so as to be proximal to aninterface 30 (i.e. a surface) of the first substrate 22. The proximityof the first waveguide 26 to the interface 30 allows the first waveguide26 to be brought into close proximity to the second waveguide 28. Itwill be appreciated that the terms “proximity” and “proximal” arerelative terms defining the position of part of the waveguide relativeto another part of the waveguide (e.g. within the same substrate) oranother waveguide (e.g. in another substrate). However, as will bedescribed herein, the waveguide configuration may allow the waveguidesin each substrate to be spaced apart while still allowing evanescentcoupling to occur between the waveguides.

The first and second substrates 22, 24 are assembled using a layer ofbonding material 32 provided therebetween. The bonding material 32 is inthe form of epoxy but in other embodiments could comprise any otherappropriate material. The bonding material 32 may be selected with arefractive index to match the refractive index of the adjacent first andsecond substrates 22, 24 (e.g. to reduce reflection losses).

The optical apparatus 20 is configured for evanescently coupling anoptical signal across the interface 30. As shown by FIG. 3, which showsa cross-sectional view orthogonal to the view of FIG. 2, the firstwaveguide 26 comprises a curved section 34 proximal to the interface 30and configured to provide evanescent coupling of the optical signalbetween the first and second waveguides 26, 28. The curved section 34extends in a plane parallel to a propagation direction of theevanescently coupled optical signal. In FIG. 3, the plane parallel tothe propagation direction corresponds to the plane of the cross-sectionof FIG. 2. In other words, the curved section 34 may be considered asextending in a plane that is perpendicular to the interface 30, e.g. aplane defined by the interface 30. In FIG. 3, the plane is perpendicularto the interface 30 and/or may be considered as corresponding to theplane of FIG. 3. Thus, in use, an optical signal can propagate betweenthe first and second waveguides 26, 28 via the interface 30 due to theevanescent coupling therebetween.

By controlling the path of the laser-inscribed first waveguide 26 todeliberately curve in the direction of coupling, the evanescent field inthe coupling region may be increased compared with non-curvedwaveguides. The curved section 34 may provide improved optical couplingefficiency between the first and second waveguides 26, 28 compared withother methods for coupling optical signals between different waveguides.The curved section 34 may allow the resulting evanescent field topropagate over a sufficient distance to permit additional layers to beprovided between the first and second waveguides 26, 28 compared with ifno curved section 34 is provided. The distance of propagationfacilitated by the curved section 34 may allow the first waveguide 26 tobe inscribed in the first substrate 22 proximal to the interface 30without necessarily forming part of the interface 30.

In this embodiment, the first waveguide 26 further comprises a straightsection 36 adjacent to the curved section 34 and proximal to theinterface 30. As will be described herein, the design of the firstwaveguide 26 may influence the coupling efficiency between the first andsecond waveguides 26, 28. A proximal portion 38 may therefore be definedas the portions of the first and second waveguides 26, 28 that areproximal to each other when the first and second substrates 26, 28 arecoupled together. In this embodiment, the straight section 36 isparallel to the proximal portion 38 of the second waveguide 28.

A radius of curvature of the curved section 34 may be defined by ageometrical relation between a portion 40 of the first waveguide 26distal to the interface and a portion (in this case, the part of thestraight section 36 adjacent the curved section 34) of the firstwaveguide 26 proximal to the interface 30. The radius of curvature ofthe curved section 34 may vary as function of position along the firstwaveguide 26. The portion 40 extends at an angle from the curved section34 away from the interface 30. It will be appreciated that the design ofthe first waveguide 26 may be arbitrary since the design depends on theparticular requirements of the optical apparatus 20. However, theportion of the first waveguide 26 proximal to the interface is shapedsuch that an evanescent field of the optical signal is permitted topropagate through the portion between the first and second waveguides26, 28.

The use of a glass or amorphous material in this embodiment as the firstsubstrate 22 may provide at least one of: an opportunity to improve theperformance, manufacturability and compatibility with PIC platforms. PICplatforms and silica may have similar thermal expansion coefficients,and may be considered to be reliable and mechanical stable. Thepossibility to use 3D laser-inscribed waveguides (e.g. such that acenterline of the laser-inscribed waveguide may extend in one, two orthree dimensions) may provide significant design freedoms (e.g.utilizing the third dimension) to improve performance and ease ofmanufacturability.

Embodiments described herein may have improved alignment tolerancescompared with other approaches. The evanescent coupling approach mayprovide lower polarization dependence compared with other approaches.The optical apparatus 10 may be relative compact (e.g. less than 200μm), for example, due to the possibility of laser inscribing the firstwaveguide 26 to be very close to the interface 30. The optical apparatus20 may be relatively straightforward to manufacture and may not requireany form of polishing in certain embodiments.

In this embodiment, the first waveguide 26 may be coupled to a standardoptical fiber (not shown). In spite of the potentially different opticalmode sizes of the optical fiber and the second waveguide 28, the designof the first waveguide 26 may be such that at least one of: lowinsertion losses, broad spectral bandwidth transmission, lowpolarization dependence and relaxed alignment tolerances can beachieved.

FIGS. 4 and 5 respectively show orthogonal cross-sectional schematicviews of an optical apparatus 50 according to a further embodiment. Theoptical apparatus 50 comprises similar features to those described inrelation to the optical apparatus 20 and the same reference numeralsshall be used for those features. However, in contrast to the opticalapparatus 20, the optical apparatus 50 does not comprise a PIC platform10 as depicted by FIG. 1.

The optical apparatus 50 comprises a waveguide layer 52 provided on theinterface 30 of the first substrate 22. In this embodiment, thewaveguide layer 52 has been etched to provide a further waveguide 54 onthe interface 30. The further waveguide 54 is positioned proximal to thefirst waveguide 26 in order to provide evanescent coupling of theoptical signal between the first waveguide 26 and the further waveguide54. In this embodiment, the further waveguide 54 comprises siliconoxynitride (SiON). It will be appreciated that other materials such assilicon nitride could be used to form the further waveguide 54. Duringmanufacture, the waveguide layer 52 is deposited on the interface 30. Apatterning process such as used in photolithography or any otherappropriate technique is used to define the shape of the furtherwaveguide 54 within the waveguide layer 52. A material removal process,such as for example etching, is then used to remove one or more parts ofthe waveguide layer 52 to leave behind the further waveguide 54.Subsequently, a cladding material 18 may be deposited on the furtherwaveguide 54 and/or exposed parts of the interface 30. The opticalapparatus 50 is an example of a standalone device for evanescentlycoupling an optical signal between the first waveguide 26 and thefurther waveguide 54. In an example, an input and/or output of thefurther waveguide 54 may be butt coupled to an external device (notshown) for sending and/or receiving between the further waveguide 54 andthe external device (and thereby facilitating optical communicationbetween the first waveguide 26 and the external device). Otherembodiments described herein comprise similar features to that of theoptical apparatus 50. However, in at least some of those otherembodiments, the “further waveguide” is provided to improve evanescentcoupling between the first waveguide and a second waveguide.

In one embodiment, the waveguide layer 52 is created using a suitabledeposition technique such as plasma enhanced chemical vapour deposition(PECVD). A pattern is then projected via a mask onto the waveguide layer52, which modifies only parts of the waveguide layer 52 that, uponremoval, leave behind the further waveguide 54. Said parts of thewaveguide layer 52 are removed, e.g. by using a material removalprocess, to form the further waveguide 54. An exemplary material removalprocess described herein may comprise etching, e.g. reactive ion etching(RIE) or wet etching, polishing, e.g. chemical-mechanical polishing(CMP), an abrasive process, e.g. abrasive blasting or sand blasting, ora combination thereof. It will be appreciated that any appropriatemethod may be used to provide the further waveguide 54 (and optionalcladding material 18) on the interface 30.

FIG. 6a shows a cross-sectional view of example waveguide configurationsfor use in the optical apparatus 50. In FIG. 6a , the upper figure showsan example shape for the further waveguide 54 and the lower figure showsan example shape for the first waveguide 26. FIG. 6b depicts therelative positioning (along the propagation direction of the opticalsignal) of the first and further waveguides 26, 54.

In this embodiment, the first waveguide 26 comprises at least onecharacteristic along the first waveguide 26 for providing adiabaticevanescent coupling of the optical signal between the first and furtherwaveguides 26, 54. The characteristic along the first waveguide 26comprises at least one phase-matching region configured such that apropagation constant of the first waveguide 26 is the same as apropagation constant of the further waveguide 54. Further, thecharacteristic is designed such that a constant loss is defined alongthe respective first and further waveguides 26, 54.

The first waveguide 26 and further waveguide 54 may comprise at leastone tapered section comprising at least one phase-matching region. Inthis embodiment, the first waveguide 26 comprises a first taperedsection 56 for providing adiabatic evanescent coupling with the furtherwaveguide 54. The first tapered section 56 has a width that variesaccording to position along the first waveguide 26.

It will be appreciated that the curved section 34 cannot be identifiedin the plan views of FIGS. 6a-6b . However, when viewed from the side,the first tapered section 56 comprises at least part of the curvedsection 34 depicted in FIG. 5. Thus, while FIGS. 6a-6b depict avariation in the characteristic (e.g. tapering) along the first andfurther waveguides 26, 54, it will be appreciated that thecharacteristic may vary along the first waveguide 26 due to the curvedsection 34. For example, the curved section 34 may comprise a taperingin both a horizontal plane (as depicted by the view of FIGS. 6a-6b ) andin a vertical plane (e.g. in a direction perpendicular to the horizontalplane). In the present example, the curved section 34 tapers inwardlytowards the interface 30 in both the horizontal and vertical plane. Itwill be appreciated that the tapering may be in only one of thehorizontal and vertical planes in some embodiments.

The first waveguide 26 may be configured in any appropriate way tofacilitate coupling of the optical signal with another waveguide (e.g. afurther waveguide 54 or a second waveguide 28 as described herein). Forexample, the refractive index of the first waveguide 26 may vary asfunction of position along the first waveguide 26. Alternatively oradditionally, the first waveguide 26 may have a refractive indexcontrast with surrounding material of the first substrate 22 that variesas function of position along the first waveguide 26.

As also shown by FIGS. 6a-6b , the further waveguide 54 comprises asecond tapered section 62 for providing adiabatic evanescent couplingwith the first waveguide 26. It will be appreciated that the design ofthe first and further waveguides 26, 54 may be varied as required. Forexample, at least one of the first and further waveguides 26, 54 maycomprise at least one tapered section, and each waveguide may havedifferent characteristics. Depending on the characteristics of the firstwaveguide 26, the further waveguide 54 may be designed such thatadiabatic evanescent coupling may be provided with the first waveguide26. Equally, the first waveguide 26 may be designed such that adiabaticevanescent coupling may be provided with the further waveguide 54.

FIGS. 7 to 8 show orthogonal cross-sectional schematic views of theoptical apparatus 50 of FIG. 4 further comprising the second substrate24 (e.g. a PIC platform 10). The optical apparatus 50 is bonded with thesecond substrate 24 using a layer of bonding material 32 and thus inthis embodiment, the second substrate 24 may be considered part of theoptical apparatus 50. It will be appreciated that in other embodimentsthe optical apparatus, e.g. the first substrate and the second substratemay be coupled or bonded together using a welding technique, such aslaser beam welding. This may avoid the use of the bonding material atthe interface between the first substrate and the second substrate.

In the present embodiment, the second waveguide 28 comprises a materialof higher refractive index than the first waveguide 26. The material ofthe further waveguide 54 comprises a material having a higher refractiveindex than the first waveguide 26 but lower than the second waveguide28.

The surface-deposited further waveguide 54 may allow fabrication ofcompact photonic components with substantially higher refractive indexcontrast compared with solely the laser inscribed first waveguide 26 andthe second waveguide 28. The optical apparatus 50 may benefit from lowloss coupling to the laser-inscribed first waveguide 26 for furtherintegration and low loss interfacing to optical fibers (not shown).Example applications include the fabrication of wavelengthmultiplexer/demultiplexer circuits on the surface waveguide layers,which may be too large to fabricate with the lower refractive indexcontrast available with other laser inscribed waveguides.

The surface-deposited further waveguide 54 may be used to allow low-lossefficient butt coupling to edge based spot size conversion couplersfabricated on high refractive index contrast platforms such as thosemade in Silicon Photonics or Indium Phosphide. It will be understoodthat one or more of the benefits of the optical apparatus 50 may beapplicable to the optical apparatus 50 with or without the secondsubstrate 24 or PIC platform 10. In other words, in some embodiment theoptical apparatus 50 (or one or more parts thereof) may be used oruseable with one or more high refractive index contrast platforms suchas those made in Silicon Photonics or Indium Phosphide.

One possible application of using the surface deposited furtherwaveguide 54 formed using the waveguide layer 52 may be to act as anintermediate layer in evanescently coupling to high refractive indexcontrast platforms. In this case, this further waveguide 54 may help toefficiently transfer the light from the first waveguide 26 into the highrefractive index contrast second waveguide 28. This approach may providefor high coupling efficiencies. Design simulations indicate that totalevanescent coupling efficiencies may be above 95%.

FIG. 9 shows a cross-sectional schematic view of an assembly of anoptical apparatus 100. The optical apparatus 100 is similar to the otheroptical apparatus 20, 50 described herein and similar features areindicated with reference numerals incremented by 100. The opticalapparatus 100 comprises a first substrate 122 and second substrate 124.The optical apparatus 100 further comprises a printed circuit board(PCB) 102. The first substrate 122 is sandwiched between the PCB 102 andthe second substrate 124. The PCB 102 comprises a carrier 104 operativeto communicate with an electrical component 168 of the second substrate124 using an electrical signal. The first substrate 124 comprises vias170 extending therethrough between the second substrate 124 and thecarrier 104. The vias 170 comprise metal contacts extending throughapertures formed in the first substrate 122. The vias 170 thereforeprovide an electrical connection between the PCB 102 and the electricalcomponent 168. The electrical component 168 is operative to convertreceived one of: the optical signal and the electrical signal into theother one of: the optical signal and the electrical signal. In otherwords, the optical apparatus 100 may function as an optical signal toelectrical signal transceiver. In this example, two waveguides 126extend from the proximal region 138 so as to be coupled into respectiveoptical devices 172 (e.g. lasers, photodiodes, or the like) viarespective optical fibers 174. Solder 176 is provided in etched recesses178 in the interface 130 are used to couple the first substrate 122 tothe second substrate 124. FIG. 9 may be considered as an example of acommunication apparatus for routing an optical signal.

FIG. 10 shows a cross-sectional view of an example configuration for thefirst waveguide 26 for use in the optical apparatus of any embodimentdescribed herein. The first waveguide 26 comprises a curved section 34.However, in contrast to FIGS. 2 to 3, the first waveguide 26 does notcomprise a similar straight section 36. The first waveguide 26 has aradius of curvature that varies as function of position along the firstwaveguide 26, which may provide for different propagationcharacteristics between the first and second waveguides 26, 28 (and/orthe further waveguide 54). The curved section 34 is such that the firstwaveguide 26 extends towards and away from the interface 30 in a planeparallel to the propagation direction of the evanescent field.

FIG. 11 shows a cross-sectional view of a further example configurationexample configuration for the first waveguide 26 for use in the opticalapparatus of any embodiment described herein. The first waveguide 26 issimilar to FIG. 10. The first waveguide 26 has a radius of curvaturethat varies as function of position along the first waveguide 26, whichmay provide for different propagation characteristics between the firstand second waveguides 26, 28 (and/or the further waveguide 54). Forexample, the evanescent field between the first and second waveguides26, 28 (and/or the further waveguide 54) may be enhanced and/or extendthe length over which sufficiently strong evanescent coupling of theoptical signal may occur. Therefore, by optimising the radius ofcurvature of the curved section 34 as function of position along thefirst waveguide 26 may provide for different, enhanced or improvedpropagation characteristics of the evanescently coupled optical signalbetween the first waveguide 26 and the second waveguide 28 and/or thefurther waveguide 54.

FIGS. 12 to 13 show various cross-sectional views of exampleconfigurations for the second waveguide 28 for use in the PIC platform10. Each depicted second waveguide 28 has a different width along thesecond waveguide 28, the design of which may depend on the design of thefirst waveguide 26 and/or their proximity and relative positioning.

FIG. 14 shows a cross-sectional view of an example configuration of thesecond waveguide 28 for use in the PIC platform of any embodimentdescribed herein. In the present embodiment, the second waveguide 28comprises a splitter 80 provided in optical communication with aplurality (two in this embodiment) of transversely spaced apart (withrespect to the interface 30) tapered sections 82 for providing adiabaticevanescent coupling with the first waveguide 26. The split structure ofthe second waveguide 28 may provide more lateral alignment tolerancecompared with if only one tapered section is provided. Thus, if therelative lateral alignment of the first and second waveguides 26, 28 isnot accurate, the additional tolerance provided by the, effectively two,second waveguides 28 may ease the alignment requirements.

FIG. 15 shows a cross-sectional schematic view of an optical apparatus200 configured to be integrated with a PIC platform according to afurther embodiment. The embodiment of FIG. 15 is very similar to theoptical apparatus 50 described herein but with similar featuresindicated by reference numerals incremented by 200. Different featuresare described herein.

The optical apparatus 200 comprises a plurality of spacing elements 284disposed between the first and second substrates 222, 224. In thisexample, the spacing elements 284 comprise silicon oxynitride but couldcomprise any other appropriate material such as silicon nitride. Afurther waveguide 254 for providing enhanced evanescent coupling isprovided between the first waveguide 226 and the second waveguide 228. Alayer of bonding material 232 is provided between a silica layer 214 ofthe second substrate 224 and a corresponding cladding material 218 ofthe first substrate 222. The spacing elements 284 may ensure that thespacing between the first and second waveguides 226, 228 and/or thefurther waveguide 254 is appropriate to provide optimum evanescentcoupling therebetween.

FIG. 16 shows a cross-sectional schematic view of an optical apparatus300 configured to be integrated with a PIC platform according to afurther embodiment. The embodiment of FIG. 16 is very similar to theoptical apparatus 200 described herein but with similar featuresindicated by reference numerals incremented by 100. Different featuresare described herein.

The optical apparatus 300 comprises a plurality of recessed regions 386in at least one layer (in this embodiment, the silica layer 314)disposed between the first and second substrates 322 and 324, whereinthe plurality of spacing elements 384 are provided in the correspondingrecessed regions 386. Providing the spacing elements 384 and recessedregions 386 may facilitate accurate and timely alignment of the first,second and further waveguides 326, 328 and 354.

FIG. 17 shows an example process flow for manufacturing the opticalapparatus of one or more of the embodiments described herein. In a firststep 400, a first substrate 22 is provided. The process flow depictsseveral different ways to manufacture the optical apparatus. In a step402 of a first process, a waveguide layer 52 is deposited on the firstsubstrate 22. In a step 404 of the first process, a first waveguide 26is inscribed in the first substrate 22. Laser inscribing after thewaveguide layer 52 (or any other layer) has been deposited on the firstsubstrate 22 may allow the first waveguide 26 to be fabricated closer tothe interface 30 than would otherwise be possible if no waveguide layer52 (or any other layer is provided). One possible reason for this may bethe reduced ablation threshold at the interface 30 resulting from theprovision of the waveguide layer 52 (or any other layer). In a second,alternative process, the order of the steps 402, 404 is swapped. Afterstep 400 in the second process, in a step 406, a first waveguide 26 isinscribed in the first substrate 22. After step 406, in a step 408, awaveguide layer 52 is deposited on the first substrate 22. After step404 or step 408, at step 410 a further waveguide 54 is formed in thewaveguide layer 52 (e.g. using a patterning process and subsequentmaterial removal process, or the like). If no further waveguide 54 isprovided, step 410 may be considered an optional step.

At an optional step 412, a layer of bonding material 32 is provided. Thelayer of bonding material 32 may be provided on the further waveguide 54and/or on another layer provided on the further waveguide 54 (forexample as depicted by FIGS. 15 to 16). At optional step 414 at leastone additional layer (such as a cladding material, or the like) isprovided. Although depicted as occurring after step 412, the at leastone additional layer may be provided before the layer of bondingmaterial 32 is provided. At optional step 416, a second substrate 24 iscoupled to the first substrate 22 (and any layers therebetween) usingthe layer of bonding material 32. The second substrate 22 may comprise asecond waveguide 28, which may be appropriately positioned with respectto the first waveguide 22 and/or the further waveguide 54 to facilitateevanescent wave coupling. The second waveguide 28 may have beenpreviously provided on the second substrate 24 (e.g. by a patterningprocess and subsequent material removal process). It will be appreciatedthat in some embodiments the second substrate 22 and/or the secondwaveguide 28 may not be provided.

After step 400 of a third process, in a step 418, a sacrificial layer(such as a cladding material 18) is provided on the first substrate 22.In step 420, laser inscription is used to provide a first waveguide 26in the first substrate 22. In a step 422, a portion of the sacrificiallayer is removed (e.g. by a patterning process and subsequent materialremoval process, or the like). In a step 424, a waveguide layer 52 isdeposited on the remaining portion of the sacrificial layer (and anyexposed portions of the first substrate 22). After step 424, at leastone of the optional steps 410, 412, 414 and 416 may be performed asdescribed herein.

It will be appreciated that the process steps of FIG. 17 could beapplied more generally. For example, a method of manufacturing anoptical apparatus may comprise providing a substrate; depositing a layeron the substrate; and laser inscribing a waveguide into the substrateproximal to an interface between the substrate and the layer. Thesubstrate may be one of a first and second substrate 22, 24. Thedeposited layer may comprise at least one of: a waveguide layer 52, acladding material 18, a layer of bonding material 32, or any otherlayer. The laser inscribed waveguide may be the first waveguide 26and/or any other waveguide. The laser inscription may be performedbefore or after deposition of the layer. The optical apparatus mayoptionally comprise a second substrate 24 comprising a second waveguide28. The optical apparatus may optionally comprise a waveguide layer 52comprising a further waveguide 54. Any modifications may be made to themanufacturing process as appropriate. For example, layers describedherein as being deposited on the first substrate 22 may be deposited onthe second substrate 24 instead, or vice versa.

It will be appreciated that the method may additionally or alternativecomprise forming the further waveguide 54 on a surface of the firstsubstrate 22 and/or second substrate 24. The method may then comprisepreparing or conditioning the surface of the first substrate 22 and/orsecond substrate 24, e.g. to reduce an amount of defects, such as forexample cracks or mircocracks, and/or particles on the surface. Themethod may comprise preparing or conditioning the surface of the firstsubstrate 22 and/or second substrate 24 prior to forming the furtherwaveguide 54. This may mitigate the use of a sacrificial layer. Thefurther waveguide 54 may be formed on the surface of first substrate 22and/or the second substrate 24, as described above, for example inrelation to step 410 of the process flow shown in FIG. 17.

In will be appreciated that in some embodiments the method mayadditionally or alternative comprise coupling the first substrate 22 andthe second substrate 24 together using a welding technique, such aslaser beam welding. This may avoid the provision of the bonding materialat the interface 30.

FIGS. 18a to 18f show cross-sectional views of exemplary waveguideconfigurations for use in the optical apparatus of any embodimentdescribed herein. It will be appreciated that the exemplary waveguideconfigurations shown in FIGS. 18a to 18f may be used in any combinationor in isolation. FIG. 18a shows an exemplary tapered section 29, 56, 62that may be part of or comprised in the first waveguide 26, the secondwaveguide 28 and/or the further waveguide 54, respectively. The taperedsection 29, 56, 62 shown in FIG. 18a comprises a width or thickness thatvaries, e.g. decreases in this example, in a first direction z and/or asecond direction. The first direction z may be considered as comprisinga direction along the first waveguide 26, the second waveguide 28 and/orthe further waveguide 54, e.g. a propagation direction of the opticalsignal in the first waveguide 26, the second waveguide and/or thefurther waveguide 54. The second direction may comprise a direction thatis perpendicular to the first direction z. It will be appreciated thatin other embodiments the tapered section of the first waveguide, thesecond waveguide and/or the further waveguide may be configured suchthat a width or thickness of the tapered section increases in the firstdirection and/or the second direction.

FIG. 18b shows an exemplary configuration of the first waveguide 26 foruse in the optical apparatus of any embodiment described herein. Thefirst waveguide 26 may be configured such that the refractive index ofpart or all of the first waveguide 26 varies, e.g. continuously varies,in the first direction z and/or second direction. For example, the firstwaveguide 26 may be configured such that the refractive index of part orall of the first waveguide 26 may decrease in the first direction zand/or the second direction, as for example shown in FIG. 18b .Alternatively, the first waveguide may be configured such that therefractive index of part or all of the first waveguide may increase inthe first direction z and/or the second direction. The refractive indexof part or all of the first waveguide may be varied, e.g. continuouslyvaried, in the first direction z and/or the second direction, byvarying, e.g. continuously varying, the refractive index contrast Δnbetween the part or all of first waveguide 26 and the surroundingmaterial of the first substrate 22. The refractive index of the part orall of the first waveguide 22 may be varied using laser inscription ofthe first substrate 22. By using laser inscription of the firstsubstrate 22, the formation of a first waveguide 26 comprising arefractive index that may vary, e.g. continuously vary, may befacilitated. It will be appreciated that the features described above inrelation to FIG. 18b may be applied to or comprised in the secondwaveguide and/or further waveguide.

FIG. 18c shows an exemplary configuration of the further waveguide 54for use in the optical apparatus of any embodiment described herein. Thefurther waveguide 54 may be configured to comprise a plurality ofsegments 54 a. The plurality of segments 54 a may be arranged along thefirst direction z. Some or all segments of the plurality segments 54 amay comprise the same refractive index. The plurality of parts orsegments 54 a may be arranged such that a refractive index, e.g. aneffective refractive index, of the further waveguide 54 varies in thefirst direction z and/or the second direction. For example, the furtherwaveguide 54 may be configured such that a size or width of some or allsegments of the plurality of parts or segments 54 a varies in the firstdirection z and/or the second direction. For example, as shown in FIG.18c , the further waveguide 54 may be configured such that the size orwidth of some or all of the plurality of segments 54 decreases in thefirst direction z and/or the second direction. This may result in therefractive index, e.g. the effective refractive index, of the furtherwaveguide 54 decreasing in the first direction z and/or the seconddirection. The further waveguide 54 may be configured such that a spaceor distance d between at least two or all segments of the plurality ofsegments 54 a varies in the first direction z. For example, as shown inFIG. 18c , the further waveguide 54 may be configured such that thespace or distance d between at least two or all segments of theplurality of segments 54 increases in the first direction z. This mayresult in the refractive index, e.g. the effective refractive index, ofthe further waveguide decreasing in the first direction z and/or thesecond direction. It will be appreciated that in other embodiments thefurther waveguide may be configured such that the size or width of someor all of the plurality of segments increases in the first direction zand/or the second direction and/or the space or distance between atleast two or all segments of the plurality of segments decreases in thefirst direction.

FIGS. 18d and 18e shows an exemplary configuration of the furtherwaveguide 54 for use in the optical apparatus of any embodimentdescribed herein. The exemplary further waveguide 54 shown in FIG. 18dis similar to that shown in FIG. 18d . However, the further waveguide 54shown in FIG. 18d may be configured such that the size or width of someor all segments of the plurality of segments 54 a is the same. Thefurther waveguide 54 may be configured such that the space or distance dbetween at least two or all parts or segments of the plurality of partsor segments is the same. The further waveguide 54 may be configured suchthat the size or width of some or all segments of the plurality ofsegment 54 a is smaller than a wavelength of the optical signal. Thefurther waveguide 54 may be configured such that the space or distance dbetween at least two or all segments of the plurality of segment 54 a issmaller than a wavelength of the optical signal in the further waveguide54. FIG. 18e shows a plan view of an exemplary configuration of thefurther waveguide 54. The plurality of segments 54 a may be arrangedalong the second direction (indicated in FIG. 18e by the y-direction).In other words, the plurality of segments 54 a, e.g. some or allsegments thereof, may be arranged to form an array of segments 54 a.Some or all of the plurality of segments 54 a may be considered asforming a metamaterial. Some or all of the plurality of segments 54 amay be arranged to vary, e.g. decrease or increase, the refractiveindex, e.g. the effective refractive index, of the further waveguide 54.It will be appreciated that the plurality of segments are not limited tothe shape shown in FIGS. 18d and 18e . For example, some or all segmentsof the plurality of segments may have any suitable shape orcross-section, such as for example a circular, elliptical, rectangular,square shape of cross-section or the like.

It will be appreciated that the features described above in relation toFIGS. 18d and 18e may equally be applied to or comprised in the firstwaveguide and/or second waveguide 28.

FIG. 18f shows an exemplary configuration of the further waveguide 54for use in the optical apparatus of any embodiment described herein.When the width or thickness of the tapered section 62 increases in thefirst direction z and/or the second direction, the further waveguide 54may comprise a constricted section 62 a. The constricted section 62 amay comprise a width or thickness, e.g. in the first direction z and/orthe second direction, that is smaller or narrower than a width orthickness of the tapered section 62, e.g. in the first direction zand/or the second direction. The constricted section 62 a may bearranged spaced or at a distance from the tapered section 62 of thefurther waveguide 54. The constricted section may be configured tofilter one or more modes of the optical signal in the further waveguide54. The constricted section 62 a may be arranged to allow transmissionof a single mode of the optical signal into the tapered section 62 ofthe further waveguide 54.

It will be appreciated that the features described above in relation toFIG. 18f may equally be applied to or comprised in the first waveguideand/or second waveguide 28.

As described above, the first waveguide according to any exemplaryconfiguration shown and described in relation to FIGS. 18a to 18f may beformed using laser inscription. The second waveguide and/or furtherwaveguide according to any exemplary configuration shown and describedin relation to FIGS. 18a to 18f may be formed using deposition and/orlithographic techniques (e.g. using a patterning and process andsubsequent material removal process), as for example described above.

Some or all of the exemplary configurations shown and described inrelation to FIGS. 18a to 18f may allow for relaxed alignment tolerances,ease of fabrication and/or compatibility with existing processes ortools in foundries.

FIG. 19 shows a cross-sectional schematic view of an optical apparatus520 according to a further embodiment. The embodiment of FIG. 19 issimilar to the optical apparatus 20 described herein but with similarfeatures indicated by reference numerals incremented by 500. Differentfeatures are described herein.

The optical apparatus 520 may comprise at least one opening 588. Theopening 588 may be part of or comprised in the first substrate 522. InFIG. 19, the optical apparatus 520 comprises three openings 588. It willbe appreciated that in other embodiments, the optical apparatus maycomprise more or less than three openings. The openings 588 may beprovided in the form of a channel, hole, through-hole, bleed-hole, ventor the like, or a combination thereof. The openings 588 may be arrangedto allow passage of gas from a space between the first substrate 522 andsecond substrate 524, e.g. when the first substrate 522 and secondsubstrate 524 are coupled together. The openings 588 may be arranged toallow passage of the bonding material 532 into at least part of eachopening 588, e.g. when the first substrate and second substrate arecoupled together, e.g. using the bonding material 532. This may allowfor control of the alignment and/or coupling between the first substrateand second substrate, e.g. control of a distance between the firstsubstrate and second substrate, and/or for the first substrate andsecond substrate to be closely brought together. The opening 588 may beformed using another material removal process, such as for example,etching, e.g. laser assisted etching, dry etching or wet etching, orablation, e.g. laser ablation, or masking.

FIG. 20 shows a cross-sectional schematic view of an optical apparatus620 according to a further embodiment. The embodiment of FIG. 19 issimilar to the optical apparatus 50 described herein but with similarfeatures indicated by reference numerals incremented by 600. Differentfeatures are described herein.

For some applications of the optical apparatus 50 or parts thereof, suchas for example in edge coupling applications, the second waveguide maycomprise a side or facet that has been conditioned using a materialremoval process, such as etching, e.g. reactive ion etching (RIE). Thismay result in a ledge-type arrangement of the second substrate 624, inwhich the second waveguide 628 is located at a distance from a firstedge 690 of the second substrate 624. In this example, the firstsubstrate 622 may be shaped or configured to allow for coupling, e.g.complementary coupling, with the second substrate 624. For example, thefirst substrate 622 may be shaped or configured to allow for buttcoupling between the further waveguide 654 provided on the firstsubstrate 622 and the second waveguide 628. For example, the firstsubstrate 622 may comprise a second edge 692. The second edge 692 may beshaped to complementarily match the first edge 690 of the firstsubstrate 624. In other words, the second edge 692 may be shaped orconfigured such that the first and second edges 690, 692 define opposingedges, e.g. to allow for complementary coupling together of the firstsubstrate 622 and the second substrate 624. This may allow for thefurther waveguide 654 being brought into close proximity of the secondwaveguide, thereby reducing a distance between the further waveguide andthe second waveguide, which may reduce losses of the optical signal overthe distance between the further waveguide and the second wave guide.The further waveguide may be formed on at least part of the second edge692. The second substrate 624 may comprise a coupling portion 694. Thecoupling portion 694 may be provided in the form of an edge coupler oredge coupling portion 694. The coupling portion 694 may be arranged toallow for butt coupling between the further waveguide 654 and the secondwaveguide 628, e.g. when the first substrate 622 and second substrate624 are coupled together. The coupling portion 694 may comprise at leastone of silicon dioxide (SiO₂) (or silica) and silicon nitride. It willbe appreciated that the coupling portion is not limited to comprising atleast one of silicon dioxide and silicon nitride and that in otherembodiments the coupling portion may comprise another suitable material.The coupling portion 694 may be configured to vary, e.g. increase, amode field diameter, e.g. to allow for butt coupling between the furtherwaveguide 654 and the second waveguide 628.

The further waveguide 654 may be arranged relative to the secondwaveguide 628 such that a propagation direction of the optical signal inthe further waveguide 654 corresponds to or is the same as a propagationdirection of the optical signal in the second waveguide 628, e.g. whenthe first substrate and second substrate are coupled together.

The optical apparatus described herein comprises a first and secondsubstrate. However, it will be appreciated that the optical apparatusmay be considered as only comprising the first substrate or onlycomprising the second substrate. The second waveguide may be regarded asan example of an additional waveguide. The further waveguide may beregarded as an example of an additional waveguide. Optical apparatusdescribed herein may comprise one or a plurality of additionalwaveguides, for example, either one or both of the second and furtherwaveguides described herein.

Various references are made to the terms “substrate” and “layer”throughout this disclosure. It will be understood that in some contexts,the terms may be interchangeable such that a layer may be considered asubstrate. In other contexts, a substrate may be considered to besubstrate.

The applicant discloses in isolation each individual feature describedherein and any combination of two or more such features, to the extentthat such features or combinations are capable of being carried outbased on the specification as a whole in the light of the common generalknowledge of a person skilled in the art, irrespective of whether suchfeatures or combinations of features solve any problems disclosedherein, and without limitation to the scope of the claims. The applicantindicates that aspects of the invention may consist of any suchindividual feature or combination of features. In view of the foregoingdescription it will be evident to a person skilled in the art thatvarious modifications may be made within the scope of the invention.

1.-37. (canceled)
 38. Optical apparatus comprising: a first substratecomprising a first waveguide formed by laser inscription of the firstsubstrate; and a second substrate comprising a second waveguide, whereinthe first waveguide comprises a curved section configured to provideevanescent coupling of an optical signal across an interface between thefirst and second waveguides.
 39. The optical apparatus of claim 38,wherein at least one of a) or b): a) the first substrate comprises atleast one of: a glass; and amorphous material; b) the first waveguidedefines a three-dimensional structure so that a centerline of the firstwaveguide extends in three dimensions.
 40. The optical apparatus ofclaim 38, comprising a further waveguide provided between the first andsecond substrates for providing evanescent coupling between the firstwaveguide and the second waveguide.
 41. The optical apparatus of claim40, wherein at least one of a), b) or c): a) the further waveguidecomprises at least one of: silicon oxynitride; germanium doped silica;and silicon nitride; b) he second waveguide of the second substratecomprises a material of higher refractive index than the first waveguideand the further waveguide, and wherein the further waveguide comprises amaterial having a higher refractive index than the first waveguide; c)the further waveguide is provided in a removed portion of a sacrificiallayer deposited on the first substrate.
 42. The optical apparatus ofclaim 38, wherein the curved section is proximal to the interface andextends in a plane parallel to a propagation direction of theevanescently coupled optical signal, and wherein the plane isperpendicular to the interface.
 43. The optical apparatus of claim 38,wherein at least one of a), b), c), d), e) or f): a) the first waveguidefurther comprises a straight section adjacent to the curved section andproximal to the interface, wherein the first waveguide is positionedrelative to the second waveguide such that the straight section isparallel to a proximal portion of the second waveguide; b) a radius ofcurvature of the curved section is defined by a geometrical relationbetween a portion of the first waveguide distal to the interface and aportion of the first waveguide proximal to the interface, wherein theportion of the first waveguide proximal to the interface is shaped suchthat an evanescent field of the optical signal is permitted to propagatethrough the portion between the first and second waveguides; c) arefractive index of the first waveguide varies as function of positionalong the first waveguide; d) the first waveguide is configured suchthat a refractive index of part or all of the first waveguide decreasesin a first direction and/or a second direction, the first directioncomprising a direction along the first waveguide and/or the seconddirection comprising a direction that is perpendicular to the firstdirection; e) the second waveguide comprises a material of higherrefractive index than the first waveguide; f) the material of the secondwaveguide comprises at least one of: silicon; silicon nitride; andindium phosphide.
 44. The optical apparatus of claim 38, comprising anelectrical component configured to at least one of: convert the opticalsignal into an electrical signal; and convert an electrical signal intothe optical signal.
 45. The optical apparatus of claim 44, wherein atleast one of a) or b): a) the electrical component is configured to atleast one of: transmit; and receive the optical signal via the secondwaveguide; b) the apparatus further comprises a carrier configured toprovide at least one of: optical, electrical and magnetic communicationwith the electrical component.
 46. The optical apparatus of claim 38,wherein at least one of a), b) or c): a) the second waveguide comprisesa splitter with a plurality of transversely spaced apart taperedsections for providing adiabatic evanescent coupling with the firstwaveguide; b) the apparatus further comprises at least one spacingelement disposed between the first and second substrates and at leastone recessed region in at least one layer disposed between the first andsecond substrates, wherein the at least one spacing element is providedin the at least one recessed region; c) a radius of curvature of thecurved section varies as function of position along the first waveguide.47. Optical apparatus for evanescently coupling an optical signal acrossan interface between a first waveguide formed by laser inscription of afirst substrate and an additional waveguide, the optical apparatuscomprising: the first substrate, wherein the first waveguide comprises acurved section configured to provide evanescent coupling of the opticalsignal between the first waveguide and the additional waveguide.
 48. Theoptical apparatus of claim 47, wherein the additional waveguidecomprises at least one of: a further waveguide deposited on the firstsubstrate; and a second waveguide of a second substrate.
 49. The opticalapparatus of claim 48, wherein the further waveguide and/or the secondwaveguide comprises a tapered section.
 50. The optical apparatus ofclaim 49, wherein the tapered section is configured such that a width ofthe tapered section increases or decreases in a first direction and/or asecond direction, the first direction comprising a direction along thefurther waveguide and/or second waveguide and/or the second directioncomprising a direction that is perpendicular to the first direction. 51.The optical apparatus of claim 50, wherein, when the width of thetapered section increases in the first direction and/or the seconddirection, the further waveguide and/or second waveguide comprises aconstricted section, the constricted section being configured to filterone or more modes of the optical signal and/or being arranged to allowtransmission of a single mode of the optical signal into the taperedsection of the second waveguide.
 52. The optical apparatus of claim 48,wherein the second waveguide is configured to comprise a plurality ofparts or segments, the plurality of parts or segments being arrangedsuch that a refractive index of the further waveguide and/or secondwaveguide varies in a first direction and/or a second direction, thefirst direction comprising a direction along the further waveguideand/or second waveguide and/or the second direction comprising adirection that is perpendicular to the first direction.
 53. The opticalapparatus of claim 38, wherein the first substrate comprises at leastone opening, the opening being arranged to allow passage of gas from aspace between the first substrate and the second substrate and/or toallow passage of a bonding material into at least part of the opening,when the first and second substrates are coupled together.
 54. Theoptical apparatus of claim 38, wherein at least one of the firstsubstrate and the second substrate is configured or shaped to allow forcomplementarily coupling with at least one other of the first substrateand the second substrate.
 55. A method of manufacturing an opticalapparatus, the method comprising: providing a first substrate; forming afirst waveguide in the first substrate by laser inscription so that thefirst waveguide comprises a curved section; providing a second substratecomprising a second waveguide; and coupling the first substrate andsecond substrate together so that the curved section is configured toprovide evanescent coupling of an optical signal across an interfacebetween the first waveguide and the second waveguide.
 56. A method ofmanufacturing an optical apparatus, the method comprising: providing afirst substrate; depositing a sacrificial layer on the first substrate;laser inscribing the first waveguide in the first substrate; removing aportion of the sacrificial layer to expose a portion of the firstsubstrate; and providing a further waveguide on the exposed portion ofthe first substrate.
 57. The method of claim 56, wherein providing thefurther waveguide comprises: depositing a waveguide layer on at leastone of: a remaining portion of the sacrificial layer and the exposedportion of the first substrate; and removing one or more parts of thewaveguide layer to form the further waveguide.
 58. The method of claim56, comprising providing a second substrate comprising a secondwaveguide, wherein the first waveguide is configured such that the firstwaveguide comprises a curved section configured to provide evanescentcoupling of an optical signal across an interface between the firstwaveguide and the second waveguide, and via the further waveguide. 59.The method of claim 56, wherein the laser inscribing step is performedone of: before the sacrificial layer is deposited on the firstsubstrate; and after the sacrificial layer is deposited on the firstsubstrate.